Systemic disease due to Candida albicans complicates many areas of progress in medicine. The pathogenesis of this organism is associated with a transformation from a yeast to mycelial phase. A mutant of C. albicans has been isolated, which is unable to form germ tubes at 37 degrees C in liquid media and is non pathogenic in animals. Wild type and mutant cultures will be grown at 250 degrees C and shifted to 37 degrees. At various times studies will be made of: a) antigens synthesized which react with reference to human or rabbit antisera; b) new proteins which are made by either the wild type or the mutant; c) possible modifications of preexisting proteins which occur at 37 degrees C in the wild type but not in the mutant; d) other biologically active products that may be made by the mutant at 37 degrees C, but not by the wild type. These studies are expected to provide information on the kinetics of synthesis of new products made during the early stages of morphogenesis. Several models for mechanisms of regulation in yeast to mycelial morphogenesis have been proposed. By comparing mutant and wild type a number of possible mechanisms will be explored.